Water-blown open-celled polyurethane foams are used in many applications, such as, for example, in automotive hoodliners and headliners. Such foams are made by both continuous and discontinuous processes to form a foam bun.
In the discontinuous process, a water-blown polyurethane foam-forming composition is deposited, often by pouring, onto a base of a large, often rectangular, box and allowed to rise and form an open-celled polyurethane foam in the box. This process is often referred to as a “bun in the box”. These buns, in many cases, can have a length of 6 to 11 feet (182 to 335 centimeters), a height of 3 to 4 feet (91 to 122 centimeters) and a width of 5 to 7 feet (152 to 213 centimeters), for example. Such a process is depicted, for example, Oertel, Polyurethane Handbook (2nd ed.) at p. 186 (1994).
In the continuous process, slabs of water-blown open-celled polyurethane foams are produced by pouring, or “laying down,” the foam-forming composition on a continuously delivered base or substrate in which the foam rises to form a bun as it is conveyed along with the base. These “slabstock” foam buns, in many cases, can have a length of 100 to 200 feet (30.5 to 61 meters), a height of 3 to 4 feet (91 to 122 centimeters) and a width of 5 to 7 feet (152 to 213 centimeters), for example. Such a process is depicted, for example, Oertel, Polyurethane Handbook (2nd ed.) at p. 178-186 (1994).
For use in subsequent production of automotive hoodliners, headliners and sun shades, the bun, whether produced by a discontinuous or continuous process, is often sliced to form a foam sheet having a thickness of, for example, ¼ inch (0.32 centimeter) to 1 inch (2.5 centimeters). Automotive headliners that include a foam sheet produced from such processes are widely used. They typically have a sandwich structure in which the foam sheet has a fiber reinforced facing adjacent to each major surface of the foam sheet. The resulting sandwich is then formed in a mold to produce a foam laminate having a concave surface, typical of an automotive headliner.
There are several important properties that an automotive headliner should possess, including a desirable aesthetic appearance, structural stiffness, acoustical properties, and energy absorption. Among these, structural stiffness has become more and more important, particularly in the case of larger headliners, such as might be present in a sport utility vehicle or mini-van, for example, as more and more accessories are commonly attached to the headliner, including storage compartments, visors, electronic systems, and the like. Structural stiffness of the foam core, therefore, is very important, since it is a major component of the headliner. It is also often desirable, such as for cost reasons, to utilize lower density foams.
One area of difficulty in producing headliners from the processes described above is that both the foam density and foam stiffness can vary significantly from the top of the bun (the foam rise side) to the bottom of the bun (the base side). Typically, foam density is higher in the bottom portion of the bun but, perhaps counterintuitively, foam stiffness is also much lower in the bottom portion of the bun than other portions with lower foam densities, which may be due to differences in foam cell geometry and/or differences in the open cell content at the bottom of the bun. This reduced stiffness limits the possibility of using lower density foams in processes to produce automotive headliners.
As a result, it would be desirable to provide methods of producing foam laminates having a concave surface, which includes a foam sheet sliced from a foam bun produced by a discontinuous box foam process or a continuous slabstock process in which the stiffness of the foam in the laminate is sufficient regardless of the location from which the foam sheet was sliced from the bun, thereby potentially enabling the use lower density foams to produce such foam laminates, which may be embodied, for example, as an automotive headliner.
The present invention was made in view of the foregoing desire.